In the past, conventional blinds for windows have typically been either venetian style blinds with transverse strips, or so called vertical blinds. These blinds could have a mechanism whereby the strips could be rotated between closed and open positions. However in the open position, in which light is transmitted into the room, there was also a loss of privacy. In the closed position, the light was obscured.
Other blinds are known which simply consist of a panel of thick flexible material, wound onto a roller in a headrail. The material can be pulled down for privacy, and to obscure the light, or raised, to allow passage of light, but with loss of privacy.
Recent developments in blind design have found that consumers are interested in obtaining blinds with a greater variety of light and dark effects, but which none the less provide for privacy.
In these types of blinds, two separate panels of blind material are provided, which may hang down over the window opening. A first translucent panel is stored on a first roller in the head rail. The material of this first panel is light permeable, but provides privacy. As a result, even when the first panel lowered, the room still receives some light.
A second blind panel is stored in the head rail and is formed of opaque material. When complete light exclusion is required this second panel can be lowered.
Both blind panels are stored in the same head rail, on separate rollers.
In another of these types of blinds, two separate panels of blind material are provided, which may hang down over the window opening. A first translucent panel is stored on a first roller in the head rail, and hangs down in a loop. The material of this first panel is light permeable, in some areas and less permeable or “dark” in other areas, but provides privacy. As a result, even when the first panel lowered, the room still receives exterior light. By varying the positions of the two portions of the loop of the first panel, it is possible to provide a greater or lesser degree of exclusion of light, and privacy.
In addition to the loop of the first panel of translucent material, these blinds also incorporate a second panel of thicker light impermeable material. This second panel is wound on a second roller in the head rail.
When this second panel is lowered, it provides for complete light exclusion, which may be desirable for sleeping.
The design of a blind header rail providing two rollers, for handling two such panels, and providing for relative movement between one portion of the first or looped panel and the other portion of the same panel, and also the provision of the second roller for the second panel, presents numerous problems. In the first place the head rail must be compact and aesthetically pleasing. Desirably the blind head rail shall occupy no more space, or only slightly more space at the top of the window opening than previously known blinds.
The operation of the two separate blind panels must be simple and capable of being operated by either manual controls, or in the case of more complex designs by means of power controls, and even remotely operated power controls.
The first or loop panel is usually translucent and usually has transverse opaque strips, spaced apart from one another, which can provide greater or lesser degrees of light transmission or exclusion. By the operation of the first roller one loop of the first panel can be moved relative to the other loop. This also provides for some degree of privacy. The transverse strips, in the two sides of the loop, can then be aligned, thus leaving open the translucent strips between them and thus allow light to permeate the two loops of the first blind panel. Alternatively the opaque strips of one part of the loop can be made to register with the translucent strips in the other portion of the loop so that more light is excluded.
In addition, it is also desirable to provide mechanism for the first roller and mechanism for the second roller in the blind head rail by which either or both of first and second panels can be raised up out of the window opening, so as to leave the window opening clear and free of the blind all together.
The blind controls are usually chains or cords, hanging down from the headrail, and controlling the first and second rollers.
One of the problems experienced with such cords is that some space must be allowed for the cord loops to hang beside one edge of the blind panels.
This space along one vertical edge of the blind panels, then allows some light in, and the blind fails to obscure all light.
Another problem is that when an operator manipulates the cords, the edges of the panels gradually become damaged. The appearance, and life, of the blind is therefor impaired.
It will be seen that this form of blind provides a front panel which is in effect two panels, one of which two panels is an intermediate panel located between the front panel and the rear panel, so that there are three panels of blind material hanging down from the one headrail.